DNA vaccination with map1 gene followed by protein boost augments protection against challenge with Cowdria ruminantium, the agent of heartwater

Th1 and Th2 epitopes of Cowdria polymorphic gene 1 of Ehrlichia ruminantium

Cowdria polymorphic gene 1 (cpg1, Erum2510, ERUM_RS01380) has been shown to induce 30% and 100% protection in sheep immunised by deoxyribonucleic acid (DNA) prime combined with DNA boost and DNA prime combined with protein boost, respectively, against heartwater infection via needle challenge. To localise its antigenic regions for inclusion in a multi-epitope DNA vaccine against heartwater, Erum2510 was cleaved into five overlapping subfragments. These subfragments were expressed individually in an Escherichia coli host expression system and evaluated for their ability to induce proliferative responses, Th1 and Th2 cytokines (interferon gamma [IFN-γ] and interleukin 4 [IL-4]) via enzyme-linked immunospot (ELISpot), quantitative real time polymerase chain reaction (qRT-PCR) and flow cytometry. Recombinant (r)proteins 3 and 4 were shown to induce immunodominant Th1 and Th2 immune responses characterised by the secretion of effector cytokines IFN-γ and IL-4 in addition to differential messenger ribonucleic acid (mRNA) expression of tumour necrosis factor (TNF), IL-2, IL-1, IL-18, IL-10, transforming growth factor (TGF), granulocyte-macrophage colony-stimulating factor (GM-CSF) and inducible nitric oxide synthase (iNOS). Thirty-seven overlapping synthetic peptides (16 mer) spanning the lengths of these immunodominant rproteins were synthesised and assayed. A peptide pool comprising p9 and p10 derived from rprotein 3 induced a Th1-biased immune response. A peptide pool comprising p28 and p29 derived from rprotein 4 induced a mixed Th1 and Th2 immune response characterised by secretion of IFN-γ and differential mRNA expression of IL-1, IL-2, IL-10, IL-12, iNOS, TGF, TNF and GM-CSF. Only one of the peptides (p29) induced secretion of IL-4. Phenotypic analysis showed significant activation of cluster of differentiation 8+ (CD8+), cluster of differentiation 4+ (CD4+) and B+ lymphocyte populations. Findings suggest that Erum2510 rproteins and synthetic peptides can induce both cellular and humoral immune responses, thereby implicating their importance in protection against heartwater.Contribution: This study will facilitate the design of an effective multi-epitope DNA vaccine against heartwater that will contribute to control this economically important disease in sub-Saharan Africa and beyond.

Protection of chicks from Newcastle disease by combined vaccination with a plasmid DNA and the pre-fusion protein of the virulent genotype VII of Newcastle disease virus

In this study, four codon optimized plasmids (designated as pCAG-optiF-1, 2, -3, and -4) containing modified F genes from the epidemic and virulent NDV genotype VII strain isolated in China that is expected to express the pre-fusion conformation of the F protein were constructed. The expression of these F variants in chicken-derived cells was detected by an indirect immunofluorescence assay and western blot analysis. Two soluble F variants (roptiF-1 and 2) potentially with the pre-fusion conformation were expressed and purified from suspended cells. Vaccination with each of the plasmids as a DNA vaccine conferred partial clinical protection to chicks against NDV. Comparatively, the plasmid pCAG-optiF-2 encoded a soluble protein with a mutant cleavage site and the potential pre-fusion conformation provided better protection than the other plasmids. Further investigation of the combined vaccinations with the plasmid DNA pCAG-optiF-2 prime + protein roptiF-2 boost vaccination strategy elicited more robust immunity, as confirmed by the detection of antibodies against NDV using enzyme-linked immunosorbent assay and virus neutralization assay, as compared to those vaccinated with only the plasmid pCAG-optiF-2 or protein roptiF-2. More importantly, the DNA prime + protein boost vaccination provided more efficacious protection against virulent NDV challenge, as evidenced by the complete clinical protection, reduced viral shedding, and limited virus replication in tissues of the challenge chicks. These results indicated that the pre-fusion conformation of the F protein could be considered as the target immunogen for the development of novel NDV vaccines.

VirB10 vaccination for protection against Anaplasma phagocytophilum

Background

Human granulocytic anaplasmosis (HGA) is a tick-borne disease caused by the etiologic agent Anaplasma phagocytophilum. HGA was designated a nationally notifiable disease in the United States in 1998. Currently there are no vaccines available against HGA. Conserved membrane proteins that are subdominant in Anaplasma species, such as VirB9 and VirB10, may represent better vaccine targets than the variable immunodominant surface proteins. VirB9 and VirB10 are constituents of the Type 4 secretion system (T4SS) that is conserved amongst many intracellular bacteria and performs essential functions for invasion and survival in host cells.

Results

Immunogenicity and contribution to protection, provided after intramuscular vaccination of plasmid DNA encoding VirB9-1, VirB9-2, and VirB10 followed by inoculation of homologous recombinant proteins, in a prime-boost immunization strategy was evaluated in a murine model of HGA. Recombinant VirB9-1-, VirB9-2-, and VirB10-vaccinated mice developed antibody responses that specifically reacted with A. phagocytophilum organisms. However, only the mice vaccinated with VirB10 developed a significant increase in IFN-γ CD4⁺ T cells and partial protection against challenge with A. phagocytophilum.

Conclusions

This work provides evidence that A. phagocytophilum T4SS VirB10 is partially protective in a murine model against infection in an IFN-γ-dependent fashion and suggests that this protein may be a potential vaccine candidate against this and possibly other pathogenic bacteria with a T4SS.

A DNA priming and protein boosting immunization scheme to augment immune responses against parvovirus in ducks

AIMS

To evaluate the effect of a DNA priming and protein boosting immunization scheme in ducks.

METHODS AND RESULTS

Pekin ducks were immunized with pTCY/VP2 DNA vaccine; on day 14 (D14) after primary immunization, the ducks were boosted with either the same vaccine (DNA + DNA) or the rVP2 vaccine (DNA + rVP2). CpG oligodeoxynucleotides containing three copies of GACGTT motifs were used as the adjuvant in the vaccines. Compared with unimmunized controls, both immunization schemes significantly increased the titre of antigen-specific antibodies, lymphocyte proliferation index, percentage of CD4⁺ and CD8⁺ cells in peripheral blood mononuclear cells (PBMCs) and mRNA expression of interferon (IFN)-α, IFN-γ, interleukin (IL)-6 and IL-12 in antigen-stimulated PBMCs. Furthermore, compared with the DNA + DNA homologous scheme, the DNA + rVP2 heterologous scheme significantly increased lymphocyte proliferation, percentage of CD4⁺ and CD8⁺ cells in PBMCs and upregulation of mRNA expression of cytokines 2 weeks after the boost (D28).

CONCLUSIONS

The DNA + rVP2 immunization scheme enhanced immune responses, mainly Th1 type, against parvovirus in ducks.

SIGNIFICANCE AND IMPACT OF THE STUDY

The DNA priming and protein boosting heterologous immunization strategy can be applied to develop vaccines against viral infections in ducks. It can potentially be used in breeding ducks because of long-term immunity may confer protection for ducklings.

Recombination and purifying and balancing selection determine the evolution of major antigenic protein 1 (map 1) family genes in Ehrlichia ruminantium

Heartwater is an economically important disease of ruminants caused by the tick-borne bacterium Ehrlichia ruminantium. The disease is present throughout sub-Saharan Africa as well as on several islands in the Caribbean, where it poses a risk of spreading onto the American mainland. The dominant immune response of infected animals is directed against the variable outer membrane proteins of E. ruminantium encoded by a polymorphic multigene family. Here, we examined the full-length sequence of the major antigenic protein 1 (map1) family genes in multiple E. ruminantium isolates from different African countries and the Caribbean, collected at different time points to infer the possible role of recombination breakpoint and natural selection. A high level of recombination was found particularly in map1 and map1-2. Evidence of strong negative purifying selection in map1 and balancing selection to maintain genetic variation across these samples from geographically distinct countries suggests host-pathogen co-evolution. This co-evolution between the host and pathogen results in balancing selection by maintaining genetic diversity that could be explained by the demographic history of long-term pathogen pressure. This signifies the adaptive role and the molecular evolutionary forces underpinning E. ruminantium map1 multigene family antigenicity.

A glycosylated recombinant subunit candidate vaccine consisting of Ehrlichia ruminantium major antigenic protein1 induces specific humoral and Th1 type cell responses in sheep

Heartwater, or cowdriosis, is a tick-borne disease of domestic and wild ruminants that is endemic in the Caribbean and sub-Saharan Africa. The disease is caused by an intracellular pathogen, Ehrlichia ruminantium and may be fatal within days of the onset of clinical signs with mortality rates of up to 90% in susceptible hosts. Due to the presence of competent tick vectors in North America, there is substantial risk of introduction of heartwater with potentially devastating consequences to the domestic livestock industry. There is currently no reliable or safe vaccine for use globally. To develop a protective DIVA (differentiate infected from vaccinated animals) subunit vaccine for heartwater, we targeted the E. ruminantium immunodominant major antigenic protein1 (MAP1) with the hypothesis that MAP1 is a glycosylated protein and glycans contained in the antigenic protein are important epitope determinants. Using a eukaryotic recombinant baculovirus expression system, we expressed and characterized, for the first time, a glycoform profile of MAP1 of two Caribbean E. ruminantium isolates, Antigua and Gardel. We have shown that the 37–38 kDa protein corresponded to a glycosylated form of the MAP1 protein, whereas the 31–32 kDa molecular weight band represented the non-glycosylated form of the protein frequently reported in scientific literature. Three groups of sheep (n = 3–6) were vaccinated with increasing doses of a bivalent (Antigua and Gardel MAP1) rMAP1 vaccine cocktail formulation with montanide ISA25 as an adjuvant. The glycosylated recombinant subunit vaccine induced E. ruminantium-specific humoral and Th1 type T cell responses, which are critical for controlling intracellular pathogens, including E. ruminantium, in infected hosts. These results provide an important basis for development of a subunit vaccine as a novel strategy to protect susceptible livestock against heartwater in non-endemic and endemic areas.

Cellular immune responses induced <i>in vitro</i> by <i>Ehrlichia ruminantium</i> secreted proteins and identification of vaccine candidate peptides

Secreted proteins are reported to induce cell-mediated immunity characterised by the production of interferon-gamma (IFN)-γ. In this study three open reading frames (ORFs) (Erum8060, Erum7760, Erum5000) encoding secreted proteins were selected from the Ehrlichia ruminantium (Welgevonden) genome sequence using bioinformatics tools to determine whether they induce a cellular immune response in vitro with mononuclear cells from needle and tick infected animals. The whole recombinant protein of the three ORFs as well as four adjacent fragments of the Erum5000 protein (Erum5000A, Erum5000B, Erum5000C, Erum5000D) were successfully expressed in a bacterial expression system which was confirmed by immunoblots using anti-His antibodies and sheep sera. These recombinant proteins were assayed with immune sheep and cattle peripheral blood mononuclear cells (PBMCs), spleen and lymph node (LN) cells to determine whether they induce recall cellular immune responses in vitro. Significant proliferative responses and IFN-γ production were evident for all recombinant proteins, especially Erum5000A, in both ruminant species tested. Thus overlapping peptides spanning Erum5000A were synthesised and peptides that induce proliferation of memory CD4⁺ and CD8⁺ T cells and production of IFN-γ were identified. These results illustrate that a Th1 type immune response was elicited and these recombinant proteins and peptides may therefore be promising candidates for development of a heartwater vaccine.

Attenuated Mutants of Ehrlichia chaffeensis Induce Protection against Wild-Type Infection Challenge in the Reservoir Host and in an Incidental Host

Ehrlichia chaffeensis, a tick-borne rickettsial organism, causes the disease human monocytic ehrlichiosis. The pathogen also causes disease in several other vertebrates, including dogs and deer. In this study, we assessed two clonally purified E. chaffeensis mutants with insertions within the genes Ech_0379 and Ech_0660 as vaccine candidates in deer and dogs. Infection with the Ech_0379 mutant and challenge with wild-type E. chaffeensis 1 month following inoculation with the mutant resulted in the reduced presence of the organism in blood compared to the presence of wild-type infection in both deer and dogs. The Ech_0660 mutant infection resulted in its rapid clearance from the bloodstream. The wild-type infection challenge following Ech_0660 mutant inoculation also caused the pathogen's clearance from blood and tissue samples as assessed at the end of the study. The Ech_0379 mutant-infected and -challenged animals also remained positive for the organism in tissue samples in deer but not in dogs. This is the first study that documents that insertion mutations in E. chaffeensis that cause attenuated growth confer protection against wild-type infection challenge. This study is important in developing vaccines to protect animals and people against Ehrlichia species infections.

Immunization with Ehrlichia P28 outer membrane proteins confers protection in a mouse model of ehrlichiosis

The obligately intracellular bacterium Ehrlichia chaffeensis that resides in mononuclear phagocytes is the etiologic agent of human monocytotropic ehrlichiosis (HME). HME is an emerging and often life-threatening, tick-transmitted infectious disease in the United States. Effective primary immune responses against Ehrlichia infection involve generation of Ehrlichia-specific gamma interferon (IFN-γ)-producing CD4(+) T cells and cytotoxic CD8(+) T cells, activation of macrophages by IFN-γ, and production of Ehrlichia-specific antibodies of the Th1 isotype. Currently, there are no vaccines available against HME. We evaluated the ability of 28-kDa outer membrane proteins (P28-OMP-1) of the closely related Ehrlichia muris to stimulate long-term protective memory T and B cell responses and confer protection in mice. The spleens of mice vaccinated with E. muris P28-9, P28-12, P28-19, or a mixture of these three P28 proteins (P28s) using a DNA prime-protein boost regimen and challenged with E. muris had significantly lower bacterial loads than the spleens of mock-vaccinated mice. Mice immunized with P28-9, P28-12, P28-19, or the mixture induced Ehrlichia-specific CD4(+) Th1 cells. Interestingly, mice immunized with P28-14, orthologs of which in E. chaffeensis and E. canis are primarily expressed in tick cells, failed to lower the ehrlichial burden in the spleen. Immunization with the recombinant P28-19 protein alone also significantly decreased the bacterial load in the spleen and liver compared to those of the controls. Our study reports, for the first time, the protective roles of the Ehrlichia P28-9 and P28-12 proteins in addition to confirming previous reports of the protective ability of P28-19. Partial protection induced by immunization with P28-9, P28-12, and P28-19 against Ehrlichia was associated with the generation of Ehrlichia-specific cell-mediated and humoral immune responses.

Animal research ethics in Africa: an overview

With research projects that use animals on the increase worldwide and in Africa in particular, animal research ethics should continue to be reviewed to improve the welfare of animals used in research. The welfare of animals used in research has gained attention globally that has led to the development of guidelines and in some instances national laws governing animal experimentation. Although there may not be empirical data on the existence or adequacy of national and/or institutional policies and guidelines on the use of animals in research in Africa, most African countries are not yet at the same level as developed countries. Consequently, some researchers based at institutions in developed countries may be tempted to 'export' their research activities to collaborating African institutions where ethical and legal frameworks on use of animals may be less stringent than in the developed countries. An appreciation of the intrinsic value of animals should be enough driving force for human beings to strive to promote humane treatment of animals. This paper gives an overview of uses and potential abuses of animals in research for the benefit of stakeholders such as researchers, research institutions, Ethics Review Committees (ERCs) and policy makers and ends with suggestions on possible ways of ensuring humane treatment of animals used in research in Africa in particular and globally in general.

Natural history of Ehrlichia ruminantium

Ehrlichia ruminantium is an obligately intracellular proteobacterium which causes a disease known as heartwater or cowdriosis in some wild, and all domestic, ruminants. The organism is transmitted by ticks of the genus Amblyomma, and it is of serious economic importance wherever the natural vectors occur, an area which includes all of sub-Saharan Africa, and several islands in the Caribbean. The disease was first recognized in South Africa in the 19th century, where its tick-borne nature was determined in 1900, but the organism itself was not demonstrated until 1925, when it was recognized to be a rickettsia, initially named Rickettsia ruminantium. It was thus the first species of what are now known as Ehrlichia to be discovered, and most of the early work to elucidate the nature of the organisms, and its reservoirs and vectors, was performed in South Africa. The next milestone was the development, in 1945, of an infection and treatment regimen to immunize livestock, and this is still the only commercially available "vaccine" against the disease. Then in 1985, after fruitless attempts over many years, the organism was propagated reliably in tissue culture, opening the way for the first application of the newly developed techniques of molecular genetics. From 1990 onwards the pace of heartwater research accelerated rapidly, with notable advances in phylogeny, diagnosis, epidemiology, immunology, and vaccine development. The complete genome sequence was published in 2005, and during the last two years a new understanding has arisen of the remarkable genetic variability of the organism and new experimental vaccines have been developed. Despite all this the goal of producing an effective vaccine against the disease in the field still remains frustratingly just beyond reach. This article summarises our current understanding of the nature of E. ruminantium, at a time when the prospects for the development of an effective vaccine against the organism seem better than at any time since its discovery 83 years ago.

Diversity of Ehrlichia ruminantium major antigenic protein 1-2 in field isolates and infected sheep

Proteins expressed from the map1 multigene family of Ehrlichia ruminantium are strongly recognized by immune T and B cells from infected animals or from animals that were infected and have recovered from heartwater disease (although still remaining infected carriers). Analogous multigene clusters also encode the immunodominant outer membrane proteins (OMPs) in other ehrlichial species. Recombinant protein analogs of the expressed genes and DNA vaccines based on the multigene clusters have been shown to induce protective immunity, although this was less effective in heterologous challenge situations, where the challenge strain major antigenic protein 1 (MAP1) sequence differed from the vaccine strain MAP1. Recent data for several ehrlichial species show differential expression of the OMPs in mammalian versus tick cell cultures and dominant expression of individual family members in each type of culture system. However, many genes in the clusters appear to be complete and functional and to generate mRNA transcripts. Recent data also suggest that there may be a low level of protein expression from many members of the multigene family, despite primary high-level expression from an individual member. A continuing puzzle, therefore, is the biological roles of the different members of these OMP multigene families. Complete genome sequences are now available for two geographically divergent strains of E. ruminantium (Caribbean and South Africa strains). Comparison of these sequences revealed amino acid sequence diversity in MAP1 (89% identity), which is known to confer protection in a mouse model and to be the multigene family member primarily expressed in mammalian cells. Surprisingly, however, the greatest sequence diversity (79% identity) was in the less-studied map1-2 gene. We investigated here whether this map1-2 diversity was a general feature of E. ruminantium in different cultured African strains and in organisms from infected sheep. Comparison of MAP1-2s revealed amino acid identities of 75 to 100% (mean of 86%), compared to 84 to 100% (mean of 89%) for MAP1s. Interestingly, MAP1-2s varied independently of MAP1s such that E. ruminantium strains with similar MAP1s had diverse MAP1-2s and vice versa. Different MAP1-2s were found in individual infected sheep. Different regions of a protein may be subjected to different evolutionary forces because of recombination and/or selection, which results in those regions not agreeing with a phylogeny deduced from the whole molecule. This appears to be true for both MAP1 and MAP1-2, where statistical likelihood methods detect heterogeneous evolutionary rates for segments of both molecules. Sera from infected cattle recognized a MAP1-2 variable-region peptide in enzyme-linked immunosorbent assay, but less strongly and consistently than a MAP1 peptide (MAP1B). Heterologous protective immunity may depend on recognition of a complex set of varying OMP epitopes.

Enhancement of humoral and cellular immunity in mice against Japanese encephalitis virus using a DNA prime-protein boost vaccine strategy

A synthetic multi-epitope gene containing critical epitopes of the Japanese encephalitis virus (JEV) envelope gene was cloned into both prokaryotic and eukaryotic expression vectors. The recombinant plasmid and purified recombinant protein (heterologously expressed in Escherichia coli) were used as immunogens in a mouse model. The results indicate that both the recombinant protein and the DNA vaccine induce humoral and cellular immune responses. Neutralising antibody titres in mice in the pcDNA-TEP plus rEP group increased considerably relative to mice immunised using either pcDNA-TEP or rEP alone (P<0.05). Furthermore, the highest levels of interleukin (IL)-2, interferon-gamma and IL-4 were induced following priming with the DNA vaccine and boosting with the recombinant protein. Together these findings demonstrate that a DNA-recombinant protein prime-boost vaccination strategy can produce high levels of antibody and trigger significant T cell responses in mice, highlighting the potential value of such an approach in the prevention of JEV infection.

Defining the immune response to Ehrlichia species using murine models

Pathogenic bacteria belonging to the family Anaplasmataceae include species of the genera Ehrlichia and Anaplasma. Ehrlichia chaffeensis, first known as the causative agent of human monocytic ehrlichiosis, also infects several vertebrate hosts including white-tailed deer, dogs, coyotes and goats. E. chaffeensis is transmitted from the bite of an infected hard tick, such as Amblyomma americanum. E. chaffeensis and other tick-transmitted pathogens have adapted to both the tick and vertebrate host cell environments. Although E. chaffeensis persists in both vertebrate and tick hosts for long periods of time, little is known about that process. Immunological studies will be valuable in assessing how the pathogen persists in nature in both vertebrate and invertebrate hosts. Understanding the host immune response to the pathogen originating from dual host backgrounds is also important to develop effective methods of diagnosis, control and treatment. In this paper, we provide our perspective of the current understanding of the immune response against E. chaffeensis in relation to other related Anaplasmataceae pathogens.

Extended immunization intervals enhance the immunogenicity and protective efficacy of plasmid DNA vaccines

Effective vaccines against infectious diseases and biological warfare agents remain an urgent public health priority. Studies have characterized the differentiation of effector and memory T cells and identified a subset of T cells capable of conferring enhanced protective immunity against pathogen challenge. We hypothesized that the kinetics of T cell differentiation influences the immunogenicity and protective efficacy of plasmid DNA vaccines, and tested this hypothesis in the Plasmodium yoelii murine model of malaria. We found that increasing the interval between immunizations significantly enhanced the frequency and magnitude of CD8+ and CD4+ T cell responses as well as protective immunity against sporozoite challenge. Moreover, the interval between immunizations was more important than the total number of immunizations. Immunization interval had a significantly greater impact on T cell responses and protective immunity than on antibody responses. With prolonged immunization intervals, T cell responses induced by homologous DNA only regimens achieved levels similar to those induced by heterologous DNA prime/ virus boost immunization at standard intervals. Our studies establish that the dosing interval significantly impacts the immunogenicity and protective efficacy of plasmid DNA vaccines.

Importance of a prime-boost DNA/protein vaccination to protect chickens against low-pathogenic H7 avian influenza infection

Control of H5/H7 low-pathogenic avian influenza (LPAI) virus circulation is a major issue regarding animal and public health consequences. To improve vaccines and to prevent vaccinated poultry from becoming infected and from shedding wild viruses, we initiated studies targeting prevention of H7 infection through DNA vaccines encoding H7 and M1 viral proteins from an Italian H7N1 LPAI virus isolated from poultry in 1999. More recently, we expressed recombinant H7 and M1 proteins in the baculovirus system to assess whether they might enhance immunity when given as a boost after DNA vaccination. The protection afforded by three vaccine combinations-DNA/DNA, DNA/protein, protein/protein-given 3 wk apart were experimentally compared in 20 specific-pathogen-free chickens per group. Ten days after the boost, chickens were challenged with a homologous (Italian H7N1 LPAI) or heterologous (French H7N1 LPAI isolated from mallards in 2001) virus. Tracheal and cloacal shedding was measured by a matrix gene (M)-based real-time reverse transcription polymerase chain reaction assay and compared with that displayed by unvaccinated infected controls. After the homologous challenge, chickens of every vaccinated group displayed a significant decrease in cloacal shedding, whereas tracheal shedding was not significantly reduced in the protein/protein group. After the heterologous challenge, only the DNA/DNA group showed a nonsignificant decrease in tracheal shedding. According to these two trials, prime-boost DNA/protein vaccination appeared be more advantageous. Further development could be aimed at improving protein expression, shifting subtype (H5), and assessing the interest of proteins as a boost of recombinant vaccines.

Protection against heartwater by DNA immunisation with four Ehrlichia ruminantium open reading frames

We have reported previously that a recombinant DNA vaccine consisting of four Ehrlichia ruminantium (Welgevonden) open reading frames (ORFs) known as the 1H12 cocktail provided protection against a virulent E. ruminantium (Welgevonden) needle challenge in sheep. In this study, we have investigated the vaccine effectiveness of two other cocktails of E. ruminantium (Welgevonden) ORFs, as well as single ORFs from the 1H12 cocktail, to protect sheep against a virulent needle challenge with the homologous strain. Each individual 1H12 ORF provided protection, but all the animals vaccinated with the other cocktails succumbed to the challenge.

Evaluation of E. ruminantium Genes in DBA/2 Mice as Potential DNA Vaccine Candidates for Control of Heartwater

Heartwater caused by the rickettsia Ehrlichia ruminantium (E. ruminantium) is an acute and fatal tick-borne disease of domestic and some wild ruminants. A user-friendly vaccine does not exist. We selected and tested nine genes of E. ruminantium for protection against challenge in a DBA/2 mouse model, in order to identify candidate genes for incorporation into a recombinant vaccine. Of the nine DNA vaccine constructs tested, four DNA constructs 14HWORF1/VR1012, 14HWORF2/VR1012, 27HWORF1/VR1012, and HSP58/VR1012 were not protective and were excluded from the study. The remaining five DNA constructs-MAP2/ VR1012, 1HWORF3/ VR1012, 4HWORF1/ VR1012, 18HWORF1/ VR1012, and 3GDORF3/ VR1012-offered partial protection against lethal challenge demonstrated by reduced mortalities compared to control groups. Protection was augmented when DNA primed mice were boosted with a respective homologous recombinant protein. Protection in these five groups was associated with the induction of cell-mediated or T helper 1 (Th1) type of immune responses characterized by the production of large amounts of interferon-gamma and interleukin-2 in in vitro proliferation assays using E. ruminantium antigens for stimulation. These responses were enhanced when the DNA-vaccinated DBA/2 mice were boosted with specific homologous recombinant protein vaccination. In a preliminary follow-up study, protection conferred by DNA vaccination with individual gene constructs was not enhanced when the protective constructs were administered in combination (including the map-1 gene of E. ruminantium). Further evaluation of these and other untested DNA constructs is necessary to optimize their expression in vivo in the presence of molecular adjuvants, such as the IFN-gamma gene, GM-CSF gene, IL-12 gene, and CpG motifs to fully evaluate their protective value.

CD8+-T-cell-dependent control of Trypanosoma cruzi infection in a highly susceptible mouse strain after immunization with recombinant proteins based on amastigote surface protein 2

We previously described that DNA vaccination with the gene encoding amastigote surface protein 2 (ASP-2) protects approximately 65% of highly susceptible A/Sn mice against the lethal Trypanosoma cruzi infection. Here, we explored the possibility that bacterial recombinant proteins of ASP-2 could be used to improve the efficacy of vaccinations. Initially, we compared the protective efficacy of vaccination regimens using either a plasmid DNA, a recombinant protein, or both sequentially (DNA priming and protein boosting). Survival after the challenge was not statistically different among the three mouse groups and ranged from 53.5 to 75%. The fact that immunization with a recombinant protein alone induced protective immunity revealed the possibility that this strategy could be pursued for vaccination. We investigated this possibility by using six different recombinant proteins representing distinct portions of ASP-2. The vaccination of mice with glutathione S-transferase fusion proteins representing amino acids 261 to 500 or 261 to 380 of ASP-2 in the presence of the adjuvants alum and CpG oligodeoxynucleotide 1826 provided remarkable immunity, consistently protecting 100% of the A/Sn mice. Immunity was completely reversed by the in vivo depletion of CD8(+) T cells, but not CD4(+) T cells, and was associated with the presence of CD8(+) T cells specific for an epitope located between amino acids 320 and 327 of ASP-2. We concluded that a relatively simple formulation consisting of a recombinant protein with a selected portion of ASP-2, alum, and CpG oligodeoxynucleotide 1826 might be used to cross-prime strong CD8(+)-T-cell-dependent protective immunity against T. cruzi infection.

Characterization of Ehrlichia ruminantium replication and release kinetics in endothelial cell cultures

Ehrlichia ruminantium is the causative agent of Heartwater, a fatal tick-borne disease affecting ruminants in African countries and West Indies and can be used as an inactivated vaccine for wild and domestic animals. In order to improve E. ruminantium production yields we characterize E. ruminantium growth kinetics in terms of duplication time, maximum production yield, and peak of infectivity. After a 24 h period for E. ruminantium attachment/internalization and a lag phase of 12 h, the exponential growth occurred within 36-108 h post-infection (hpi) with a net increase of up to 2.2 orders of magnitude. Maximum E. ruminantium infectivity was observed at 120 hpi and was defined as the best time of harvesting (TOH) for propagation of E. ruminantium cultures. This study showed that considering the quality constraint of the final product (E. ruminantium vaccine), the E. ruminantium suspension should be harvested at 113 hpi. Overall, the characterization of E. ruminantium progression through the average infection cycle, not only can contribute to the maximization of E. ruminantium production yield, with important consequences for the large scale production and utilization of an inactivated Heartwater vaccine, but also to elucidate growth mechanisms of some of the other ehrlichial species, with emerging impact in human and animal health.

Enhanced breadth of CD4 T-cell immunity by DNA prime and adenovirus boost immunization to human immunodeficiency virus Env and Gag immunogens

A variety of gene-based vaccination approaches have been used to enhance the immune response to viral pathogens. Among them, the ability to perform heterologous immunization by priming with DNA and boosting with replication-defective adenoviral (ADV) vectors encoding foreign antigens has proven particularly effective in eliciting enhanced cellular and humoral immunity compared to either agent alone. Because adenoviral vector immunization alone can elicit substantial cellular and humoral immune responses in a shorter period of time, we asked whether the immune response induced by the prime-boost immunization was different from adenoviral vaccines with respect to the potency and breadth of T-cell recognition. While DNA/ADV immunization stimulated the CD8 response, it was directed to the same epitopes in Gag and Env immunogens of human immunodeficiency virus as DNA or ADV alone. In contrast, the CD4 response to these immunogens diversified after DNA/ADV immunization compared to each vector alone. These findings suggest that the diversity of the CD4 immune response is increased by DNA/ADV prime-boost vaccination and that these components work synergistically to enhance T-cell epitope recognition.

Augmented humoral and cellular immune responses of a hepatitis B DNA vaccine encoding HBsAg by protein boosting

Several reports have indicated that combinatorial regimens with DNA and protein vaccines can elicit both strong immune responses, to circumvent the limits of each vaccine. Surprisingly little was known on HBV vaccine. Here, we investigated the immunization effects of several regimens in BALB/c mice. The level of total antibody and isotypes of IgG were determined by ELISA. Cellular immune responses were assayed by measuring the production of cytokines and CTL activity after re-stimulation for 7 days in vitro with tumor cells CT26/S stably expressing HBsAg. The efficacy of immunoprotection against the challenge of transplanted CT26/S was also examined. The regimen involving twice priming pVAX(S) encoding HBsAg and once recombinant HBsAg protein (rHBsAg) boosting, induced strong and homogenous antibody responses. This regimen induced significant stronger responses of interleukin-12 and gamma interferon (IFN-gamma) in splenocytes, and elicited stronger CD8+ CTL responses and greater immunopretectional efficacy than those elicited by immunization with rHBsAg or pVAX(S) alone. Our regimen may thus provide a strategy for developing an improved immunization against HBV and many other pathogens.

Improved immunogenicity of a tuberculosis DNA vaccine encoding ESAT6 by DNA priming and protein boosting

The study evaluated the immune response elicited by a DNA vaccine encoding ESAT6 protein of Mycobacterium tuberculosis by DNA prime-protein boost protocol. BALB/c mice were respectively vaccinated with plasmid DNA encoding ESAT6 protein, with ESAT6 protein in IFA adjuvant, or a combined DNA prime-protein boost regimen. While DNA immunization induced Th1-polarized immune response, protein-in-adjuvant vaccination elicited a Th2-dominant response. When animals were primed with DNA and boost with protein, both antibodies and Th-cell proliferative response were significantly enhanced. Moreover, production of Th1-type cytokine (IFN-gamma) was increased significantly by DNA priming-protein boosting. This protocol also resulted in an increased relative ratio of IgG2a to IgG1 and the cytotoxicity of T cells. Thus, this study demonstrated that the formation of ESAT6 DNA prime-protein boost inoculation could improved antigen-specific cellular immune responses, which are important for protection against TB infection.

Analysis of Ehrlichia ruminantium-specific T1/T2 responses during vaccination with a protective killed vaccine and challenge of goats

Ehrlichia ruminantium is an obligate intracellular bacterium that causes heartwater in ruminants and for which T-cell-mediated immunity is believed to play an important role in protection. To better characterize protective cellular immunity, E. ruminantium-specific IFN-gamma and IL-4 recall responses in major T-cell subsets were analysed by flow cytometry during immunization of goats with a killed vaccine and following a virulent challenge. The killed vaccine elicited both CD8+ and CD4+ subsets to produce cytoplasmic IFN-gamma in the absence of IL-4, thus indicating a biased T1 response. The relative capacity of CD8+ T-cells to produce IFN-gamma was significantly higher than CD4+ T-cells but the final contribution of both subsets was comparable. Circulating ER-specific CD4 and CD8 effectors substantially decreased in numbers after the booster injection and could not be detected in most animals during challenge, which warrants further investigation in immune compartments other than blood. Since IFN-gamma inhibits the growth of the pathogen in target cells, the information provided in this study on E. ruminantium-specific T1 responses will be valuable to develop cellular tools for the identification of potential protective antigens.

DNA vaccines for non-infectious diseases: new treatments for tumour and allergy

The last decade of DNA vaccine research was characterised by a pioneer spirit and enormous enthusiasm, with a large number of publications demonstrating the usefulness of this approach. Unfortunately, DNA vaccines have not necessarily met the high clinical expectations and a number of complications need to be overcome. In the case of cancer and allergy, the requirements for achieving the objectives are very different. Vaccines against allergies need to suppress or alter an unwanted immune response, while a cancer DNA vaccine has to overcome tolerance and/or immune suppression and initiate a powerful immune response. This review addresses currently used general optimisation strategies for DNA vaccines such as modification of immunisation regimens, improving the delivery systems and using molecular adjuvants. In addition, cancer-specific approaches, such as the stimulation of innate and adaptive immunity with replicase-based DNA vaccines, and targeting non-tumour-associated antigens (TAAs) are discussed. Specifically for the optimisation of DNA vaccination against allergies, procedures such as allergen gene recoding, T helper (Th)1 modulation, and the creation of safe DNA vaccines by gene fragmentation, ubiquitination or using artificial hypoallergens are being analysed. These strategies, individually or in combination, hold the potential of making DNA vaccines useful for application in the clinic.

A DNA-priming protein-boosting regimen significantly improves type 1 immune response but not protective immunity to Trypanosoma cruzi infection in a highly susceptible mouse strain

BALB/c or C57Bl/6 mice immunized with plasmids containing Trypanosoma cruzi genes developed specific immune responses and protective immunity against lethal parasitic infection. In contrast, in the highly susceptible mouse strain A/Sn, DNA vaccination reduced the peak parasitemia but promoted limited mouse survival after challenge. In the present study, we tested whether the immunogenicity and protective efficacy of vaccination could be improved by combining DNA and recombinant protein immunization regimens. A/Sn mice immunized with plasmid p154/13 which harbours the gene encoding Trypanosoma cruzi trans-sialidase developed a predominant type 1 immune response. In contrast, immunization with the recombinant Trypanosoma cruzi trans-sialidase protein adsorbed to alum generated a typical type 2 immune response. Simultaneous administration of both p154/13 and recombinant Trypanosoma cruzi trans-sialidase protein also led to a predominant type 2 immune response. Sequential immunization consisting of two priming doses of p154/13 followed by booster injections with recombinant Trypanosoma cruzi trans-sialidase protein significantly improved specific type 1 immune response, as revealed by a drastic reduction of the serum IgG1/IgG2a ratio and by an increase in the in vitro interferon-gamma secretion by CD4 T cells. Our observations confirm and extend previous data showing that a DNA-priming protein-boosting regimen might be a general strategy to enhance type 1 immune response to DNA vaccines. Upon challenge with Trypanosoma cruzi, no improvement in protective immunity was observed in mice immunized with the DNA-priming protein-boosting regimen when compared to animals that received DNA only. Therefore, our results suggest that in this experimental model there is no correlation between the magnitude of type 1 immune response and protective immunity against Trypanosoma cruzi infection.

Preparation of Ehrlichia ruminantium challenge material for quantifiable and reproducible challenge in mice and sheep

The causative agent of heartwater, Ehrlichia ruminantium, is a tick-transmitted pathogen that infects bovine endothelial cells. Due to the obligate intracellular nature of this organism obtaining pure material in sufficient quantities for challenge studies is difficult. A murine model is frequently used to study potential vaccine candidates but giving reproducible challenges in this model for heartwater has always been problematic. We have therefore performed a series of experiments to optimize the parameters governing the reproducibility of challenge material. Two cryoprotectants were compared for the preparation of challenge material, buffered lactose peptone (BLP) and sucrose-potassium-glutamate (SPG). In addition two sources of virulent E. ruminantium were used, infected bovine endothelial cultures and infected mouse spleen homogenates. We also examined practical parameters affecting the reproducibility of challenge experiments: the time it takes to deliver the challenge material, the length of time a mouse remains immune to E. ruminantium challenge, and the effect of a given challenge dose. Finally, we performed a pilot study to determine whether mice could be used to titrate challenge material to be used for experiments in sheep. We found that: (a) E. ruminantium-infected mouse spleen homogenate provides more reproducible challenges than tissue culture material; (b) SPG is a better cryoprotectant than BLP; (c) challenge material should be used within 20min of thawing; (d) it is not essential to use syngeneic material for murine challenge experiments; (e) Balb/c mice are more sensitive to E. ruminantium challenge than C57BL/6J mice; (f) mice immunized by infection and treatment for use as positive immune controls should be challenged within 3 months of immunization; and (g) mice should be challenged with a dose not exceeding 10 LD(50)s.

Babesiosis and heartwater: threats without boundaries

Suppose one of your clients from southern Florida starts talking about cattle egrets while you are vaccinating her cat. It seems she found a nearly dead egret near the cattle pen a few days ago, picked it up, and noticed a number of what looked like small ticks on the legs. Or, suppose you are called out to a small dairy in central Texas to look at some cows that are feverish and anemic. The first animal you examine has a few brown ticks attached just under the tail. Finally, perhaps you are looking at a lame tortoise for a reptile fancier, a new client, and find a large, colorful tick on a hind leg, well up under the shell. Ring any bells? Egrets are great hosts for the immature stages of Amblyomma ticks and have been captured and marked in the eastern Caribbean, then recaptured in the Florida Keys. Those cattle ticks in Texas might be acaricide-resistant Boophilus ticks that originated in Mexico. The Amblyomma tick on the tortoise could well have "hitch-hiked" all the way from South Africa. By now you remember that both Amblyomma and Boophilus ticks are efficient vectors of two tickborne diseases in this hemisphere, heartwater (in the case of Amblyomma) and babesiosis (transmitted by Boophilus ticks). Both of these diseases are exotic to the United States, and because our livestock are considered to be totally susceptible, an introduced infection could result in high initial death losses (approximately 70%); thus, both the ticks and the diseases pose immediate threats to the health and economic security of United States animal industries. Most importantly, you, whether as a small animal or large animal practitioner, are the first line of defense against such exotic diseases and their vectors.